There is international concern about the amount of airborne toxic materials found in shooting ranges, particularly airborne lead. For example, the Federal Government of West Germany has set the maximum permissible work-place concentration of lead dust at 0.1 mg of lead per cubic meter of air. During tests at German and non-German shooting ranges, equipped with various types of ventilation systems, concentrations of up to 9 mg of lead per cubic meter were measured over exposures of 4-6 hours when conventional, fully jacketed 9.times.19 mm Luger (parabellum) ammunition was used. High concentrations of airborne lead are also found in some indoor shooting ranges using .22 caliber ammunition. The main problem is thought to come from the lead styphnate and barium nitrate used in the priming compositions.
One attempt to solve the above problem for centerfire ammunition (which has primer cup or Berdan primer placed in the center of the cartridge base) has been the "Sintox" primer developed by Dynamit Nobel of Troisdorf, West Germany which is thought to use an amorphous dinol initiating explosive mixed with zinc and titanium compounds rather than lead or barium compounds. However, that priming composition is not suitable for priming rimfire cartridges because it does not easily flow into the rim of the cartridge during the priming procedure. Also, rimfire primer mixes must have much higher sensitivity than centerfire primer mixes and it is thought that "Sintox" does not have sufficient sensitivity for use in .22 caliber rimfire. Dinol having a smaller crystalline size than that of the "Sintox" primer was made and was tried by applicant's predecessors at Olin Corporation about 40 years ago, but that mix contained lead in forms of lead thiocyanate an lead peroxide and is thus not suitable as a lead-free primer mix. Thus, a need remains for a lead-free primer mix for .22 caliber rimfire cartridges.
Also of concern is the bullet. Caliber .22 bullets are conventionally made of lead which is sometimes plated with copper for aesthetic reasons. There is a concern that some of the airborne lead found in indoor shooting ranges may be caused by vaporization of the lead base of the bullet, frictional wear during passage of the bullet through the barrel or air and/or "dusting" (or minute fragmentation of the lead bullet) upon impact of the lead bullet with the target or backstop. Copper bullets, aluminum bullets and other non-lead bullets are known as a solution to the concern about airborne lead from the bullet.
A solution to this problem of needing a sensitive lead-free, non-toxic .22 caliber rimfire primer has been long sought after. Rimfires have been in existence for many many years without such a primer having been found. It is well known that rimfire priming mixes must have a considerably greater sensitivity than that required by centerfire primers, so even if a low sensitivity lead-free centerfire primer mix is found, it is not obvious how to make a high sensitivity lead-free, non-corrosive, non-toxic rimfire priming mix. The phase "Non-toxic" as used herein means consisting essentially of materials which are not heavy metals such as lead or barium and not known carcinogens or poisons, especially when vaporized, burnt or exploded as in the firing of an ammunition round. "Lead-free" as used herein means having no lead except for insignificant impurities. "Non-corrosive" as used herein means not containing halogens and thus producing any significant combustion products which are corrosive to iron or steel barrels. The problem is such that the U.S. Government's Army Research and Development Center issued a contract to Olin to study the feasibility of developing such a primer.
A solution to the above problem is achieved by the present invention which provides a priming method for producing rimfire cartridges, which includes the steps of introducing a quantity of non-toxic, non-corrosive, lead free priming material into an empty rimfire ammunition shell case; spinning the shell case so as to centrifugally force the priming material into a rim of the rimfire shell case; introducing a quantity of propellant into the interior of the base of the shell case adjacent to the centrifugally located primer material and then densifying and stabilizing the position of the densified propellant sufficiently that it will remain adjacent to the priming material until the priming material is detonated; introducing a quantity of loose propellant powder into the interior of the shell case forward of the priming material and densified propellant material; sealing the open end of the shell case so as to confine the loose propellant there within.